Multi-User Dungeons (MUD's)

A
class of virtual reality experiments accessible via the
Internet. These are real-time chat forums with structure;
they have multiple 'locations' like an adventure game,
and may include combat, traps, puzzles, magic, a simple
economic system, and the capability for characters to build
more structure onto the database that represents the existing
world.

Multi-User Dungeons (MUD's) are one of the most unique and entertaining
inventions on the Internet.
Each MUD is a virtual universe run by a complex server program
which manages a local world in response
to the words and actions of human and automated visitors. The following
sections provide more information.